1. Field of the Invention
The present invention relates to an optical device and a projector.
2. Description of Related Art
Conventionally, projectors including a plurality of optical modulators for modulating light beams emitted from a light source according to image information and forming an optical image, a color combining optical device for combining the light beams modulated by the optical modulators into a light beam and a projection optical device for enlarging and projecting the light beam combined by the color combining optical device are known.
Of the above listed components, the optical modulators are generally realized by using an active matrix drive type optical modulators formed by filling a gap between a pair of substrates with an electro-optic material such as liquid crystal and hermetically sealing the gap. More specifically, the paired substrates of the optical modulator include a drive substrate arranged at the light beam emitting side to apply a drive voltage to the liquid crystal, data lines, scanning lines, switching elements and pixel electrodes being formed thereon, and an opposite substrate arranged at the light beam incident side on which a common electrode and a black matrix are formed.
A light beam incident-side polarization plate and a light beam irradiation-side polarization plate that transmit light beams having a predetermined polarization axis are arranged respectively at the light beam incident side and the light beam emitting side of the optical modulator.
When the optical modulators are irradiated with the light beams that are emitted from the light source, the temperature of the optical modulators is apt to rise due to absorption of light by a liquid crystal layer as well as by the data lines and the scanning lines formed on the drive substrate and also by the black matrix formed on the opposite substrate. Additionally, of the light beams emitted from the light source and the light beams transmitted through the optical modulators, those that do not have a predetermined polarization axis are absorbed by the incident-side polarization plate and the irradiation-side polarization plate. Therefore, the polarizing plates are apt to emit heat.
Thus, projectors containing such an optical element and provided with a cooling device using a cooling fluid for the purpose of reducing the temperature rise of the optical element have been proposed (see, for example, Reference Document 1: Japanese Patent Laid-Open Publication No. Hei 3-174134).
The cooling device described in Reference Document 1 has a substantially cubic cabinet having a pair of oppositely disposed open end facets and a cooling chamber contained in the cabinet and filled with cooling fluid. An optical modulator is arranged at one of the oppositely disposed open end facets and a incident-side polarization plate is arranged at the other open end facet to close the open end facets respectively by the optical modulator and the incident-side polarization plate, thereby forming the cooling chamber. With the above-described arrangement, the heat generated in the optical modulator and the incident-side polarization plate by the light beam irradiated from the light source is directly discharged into the cooling fluid.
However, since cooling fluid is filled in the cooling chamber and the cooling chamber is hermetically sealed in the cooling device described in Reference Document 1, the cooling fluid is apt to be heated by the optical modulator and the polarizing plate that emit heat so that the warmed cooling fluid remains in the cooling chamber. Therefore, there is a problem that the temperature difference between the optical modulator and the cooling fluid becomes small to make it difficult to efficiently cool the optical modulator.
Reference Document 2 (Japanese Patent Laid-Open Publication No. 2003-233441) describes a liquid cooling system proposed to dissolve the above-identified problem. According to Reference Document 2, the cooling fluid in the cooling chamber is guided to the outside and then returned to the cooling chamber so as to make the cooling liquid always circulate.
The liquid cooling system described in the Reference Document 2 has a pump, a jacket and a reserve tank mounted on a heat emitting plate and the pump, the jacket and the reserve tank are connected to each other by way of pipes to allow the cooling fluid to circulate. Thus, as such a liquid cooling system is incorporated into a projector as described in Reference Document 1 or the jacket of the liquid cooling system is replaced by a cooling device as described above, it is possible to forcibly flow in and flow out the cooling fluid by the pump and cause the cooling fluid to constantly flow through the cooling chamber in order to avoid warmed cooling fluid remaining in the cooling chamber and efficiently cool the optical modulator.
However, when the liquid cooling system as described in Reference Document 2 is incorporated into the projector as described in Reference Document 1, the liquid cooling system that is dimensionally large provides a handling disadvantage. Then, it is difficult to place the optical modulator at the right position relative to the optical axis of the light beam emitted form the light source. When the optical modulator is displaced from the right position relative to the optical axis of the light beam emitted from the light source as described above, unnecessary light is projected on the screen.